The interaction of electromagnetic radiation with materials is a well-studied field, and has led to significantly valuable contributions in the areas of optical displays, optical filters, the optical transmission and storage of information, and the like. See, for example, E. Yablonovitch, “Photonic Crystals,” Scientific American, December 2001, pp. 47-55. While the potential of electromagnetic crystal structures and metallo-dielectric structures is very high, methods of forming these materials may be complex and difficult to transfer to manufacturing,
Methods of forming structured optical materials range from constructing materials with voids and filling those voids (see, for example, U.S. Pat. No. 6,139,626 to Norris et al., issued on Oct. 31, 2000; and V. Colvin, From Opals to Optics, Photonics and Electromagnetic Crystal Structures IV, Abstract Book, p. 23, Oct. 28-31, 2002, Los Angeles, Calif.) to the printing of metallic patches on dielectric layers to form artificial dielectrics. Applications of nanostructured materials include, for example, RF antennas and reflectors, nanoscopic lasers, optical filters, optical switches, displays, materials for glare reduction, and materials for stealth coatings for military equipment.
Optical filters may be constructed in a variety of ways. One type of optical filter uses layers of non-conductive materials of differing dielectric constants. In this approach, incident light, which may be polychromatic, passes through a first material of first dielectric constant, to an interface with a second material characterized by a second dielectric constant. If the second dielectric constant is greater than the first dielectric constant, then a portion of the incident light may be reflected back through the first material. If the difference in dielectric constant between the two materials is large, then a significant portion of the incident light may be reflected. The magnitude of the reflected light may be dependent on, for example, whether the returning light is in or out of phase with the transmitted light. Thus, the magnitude of the reflected light may be a function of at least the wavelength of the incident light, path length through the first material, dielectric constant of the first material, and/or the difference in dielectric constant between the first and second materials.
Optical filters having various arrangements of multiple layers may be constructed where the dielectric constant of the various layers, pathlengths through various layers, and the like are selected such that the overall arrangement filters out light of one or more selected wavelengths, while allowing passage of one or more different wavelengths. Certain filters can be constructed such that light of only a narrow wavelength is transmitted, so that light of only a narrow wavelength is reflected, and/or essentially any combination of predetermined reflected and transmitted light.
Another optical filter technique involves the use of metals and/or other conductive surfaces. In this approach, light may be transmitted through a first material of a first dielectric constant, to a second material of a second dielectric constant. A thin metal film can be used to separate the first and second materials. At boundaries where the dielectric and conductive properties of the materials change abruptly, the propagation of electromagnetic waves at the boundary may result in a boundary charge wave. The collective excitations of electrons (i.e., the charge wave) at the interface on which the metal film is deposited is typically referred to as surface plasmons. At a certain angle (and at a predetermined polarization), the interaction between the transmitted or evanescent waves, and the surface plasmon may satisfy a certain resonant condition. For example, at a certain angle, incident light may couple with the surface plasmon of the metal layer and maximize the magnitude of the transmitted light relative to the reflected light. Similarly, at a particular angle, the reflected light may be at a maximum. The minima and/or maxima of transmitted or reflected light typically are a function of the thickness of the metal film, the dielectric constant of the second material, and/or the angle or wavelength of the incident light. Properties such as the thickness of the metal and/or the dielectric constant of the second material can be adjusted in many cases to tailor the wavelength of the transmitted or reflected light. For example, these properties can be adjusted to create a filter that allows the transmission of a narrow band wavelength of light, to reflect only a narrow wavelength of light, or the like.
Optical displays can take a variety of forms. In several types of optical displays, an image is comprised of many pixels which, when selectively turned on or off, or varied in color, produces an overall image. For example, a display may include a matrix having a large number of light emitters which, when selectively turned on or off, or varied in color, produces an image. As another example, electroluminescent displays involve many tiny electrochemical components arranged in a matrix. When various of the components are electronically activated, they can emit light of a particular wavelength, creating an overall image across the display. In some displays, each pixel comprises three different light emitters, representing the three primary colors. For each pixel, activation of one or more of the emitters, at one or more predetermined intensities, can create emission of light of essentially any color from that pixel. An array of pixels, arranged in a matrix in a display, can provide the ability to display essentially any image. In other displays, the emitters emit “white” light and filters provide the same capability of generating light comprised of a predetermined quantity of each of the primary colors.
In some applications where glare reduction is desired, one common technique for glare reduction is to vary (e.g., randomly) the thickness of a glare-resistant layer over another surface. For example, glare-resistant glass for use over pictures typically is a glass layer of varying thickness which can cause random light scattering and/or random reflection of light of various wavelengths, such that no single “glare” mode of reflected light can be maximized. In another technique for glare reduction, materials of varying dielectric constants are layered at different thickness, such that light reflected off the material is not in phase, such that destructive interference of the light diminishes the magnitude of the reflected light.
In another technique for glare reduction, a surface is made glare-resistant by coating it with a polymer mixture that results in islands of polymer distributed across the surface. The polymer mixture can include a first type of polymer that adheres to the surface, and a second, segregating polymer which, through incompatibility with the first polymer, or the like causes segregation of the first polymer into individual or separate regions. The first polymer may be provided with chemical functionality, causing it to adhere to the surface, while the second polymer may be of a chemical functionality that allows it to be rinsed away or otherwise removed after polymer segregation. Alternatively, the second polymer may remain on the surface to separate the first polymer into individual or separate regions. In many cases, tiny “islands” or regions of polymer are produced that are distributed across the surface, which can cause random light scattering, similar to the above-described glare-resistant picture glass. In some cases, a random distribution of polymer may define altered dielectric constants, which can cause destructive interference of transmitted or reflected light of a predetermined wavelength or random wavelengths, thus minimizing glare. In certain instances, a random distribution of polymer can result in other altered optical properties that can reduce glare.